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I have a air handler in the attic, part of a Hyrdo Air system, not quite sure of the size. The unit short cycles, comes on for 10 seconds or so, goes off, does it again, then on for a short period of time.

The unit also produces a whistling noise in some of the rooms in the second floor. I had my service company out to look at it, they added a return, but the problems seem to be getting worse. Any suggestions!

have a competant hvac contractor out to do a manual J and a ,manual D to determine if you have an oversized unit and to determine the proper duct size for your unit. It sounds like you have an oversized unit and ductwork that is to small

Short cycling of air handlers can be many reasons, but if the fan is controlled by an aquastat, making a tuning adjustment to that will eliminate short fan cycles. Thermostat settings can reduce or eliminate short cycling as well. Call a pro.